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Theme: paints and finishes

1 April, 2003 | By Sutherland Lyall

Fashion is always strong in the paint sector, with demand for an ever-changing choice of colours. But behind the scenes, the technicians grapple with the physics and chemisty of providing long-lasting protection against the elements Take a look at early 20th century architectural specifications. In the painting clauses will be complete instructions about how white lead has to be mixed with so much linseed oil and turpentine and so much pigment, and for how long the resulting paint has to be stirred and kept in airtight containers.

This was real-life stuff, based on experience and not copied off the back of a manufacturer's brochure. Those, too, were the times of water-based distemper, when pigmented ground-up chalk was mixed with water plus a little binder and slapped on with a big brush. And that, with some specialist exceptions, was all that architects needed to know about paints and coatings.

A look at the current generic list in the British Coating Federation's product finder at www. coatings. org. uk might spur a sudden urge to be back in those simpler times. What architects have necessarily traded for a mass of experience with one or two traditional paint types is heavy reliance on the technical specifications of a smorgasbord of contemporary coating systems.

Poisonous white lead has disappeared from modern paints, various acrylic and alkyd-based paints have emerged, and now the big move is in the direction of waterbased paints that look and perform like oilbased coatings. This seems to be attempting the impossible, or at least doing an old thing in a totally different way, and, not surprisingly, involves some very heavy and ingenious chemistry. Quite a lot of this has already been carried out in Europe, where the pro-water movement is strong - Switzerland actually levies heavy taxes on spirit-based paints.

And, ever driven by fashion, paint companies are sprucing up their ranges as specifiers call for more imaginative colours.

Any colour as long as it's green It is not, of course, as simple as that.

Construction Resources, the green London building merchant, argues that the new water-based paints contain 'more chemicals than the oil-based paints they are intended to replace', some of which evaporate a long time after painting. It also says vinyl-resin-based emulsion paint can be harmful.

It argues for natural paints - based on linseed oil, turpentine, earth pigments, chalk, d-limonene (oil extracted from crushed citrus-fruit skins) and lime. Among the virtues of these ingredients is the fact that they are derived from either plentiful sources or renewable living materials: chalk and lime from the ground, the oils from plants and trees.

Colour-conscious designers might be frustrated at the very limited range and intensity of colours available from both the otherwise very imaginative Construction Resources (www. constructionresources.

com) and The Green Building Store in rural Yorkshire (www. greenbuildingstore. co. uk).

The umbrella group for green building products, the Association for Environment Conscious Building at www. aecb. net/ index. htm, has further general details.

Its Flat Matt range used to be available in white and in the RIBA Drawings Collection range, but now it comes in all the Crown Trade colours. Flat Matt is flatter and matter than ordinary matt paint and apparently represents a shift in fashion from formerly popular silk finishes. Previously, the flattest paints were oil-based, not the matt emulsions, which always have a slight sheen.

The new Crown colours all comply with British Coatings Federation (and the European CEPE) recommended levels for volatile organic compounds (VOCs), which for Flat Matt are 30g/litre. Crown's RIBA Drawings Collection's range has been enlarged. The most recent 15-colour palettes to be added to the existing six are Art Deco and Regency colours. The former washable flat matt emulsion range is inspired by drawings by Art Deco-ist John Alexander. The regency colours are inspired by drawings by the architect Alexander Roos, who had in turn been inspired by the early excavations at Pompeii. Acrylic eggshell is available for woodwork in both ranges. Check it all out at www. historic-colours. co. uk. The main Crown site is at www. paintspec. co. uk.

Spots before the eyes There is always a market for specialist paints, and from ICI Dulux Trade comes the multifleck system. A water-based base coat, available in 30 colours, is applied using any of the common methods, followed by a waterbased topcoat in five broken multifleck colour effects, which can only be sprayed.

There is a washable, protective clear coat in matt, satin and gloss finishes. Dulux claims that the topcoat goes '2.5 times further than that of competitors', which could well be the case, since the top coat is made up of flecks.

Braving the elements Although clients have always thought it reasonable to ask for maintenance-free external skins for their buildings, this ideal has remained elusive. In the wrong weather conditions, and especially in the moist British climate, it seems inevitable that water will penetrate, stone and brick surfaces will spall, walls made from them will fissure, timber deteriorate, and renders crack.

So paint as it was once understood is not enough. Now it has not only to provide a coloured surface but also serve functions such as accommodating movement, resisting microbiological attack, holding steady chemical balances in the substrate, and defending the integrity of the structure from things like carbonation and efflorescence.

Coatings scientists have to investigate at the molecular level and need a fierce understanding of the chemistry and physics of substrates. And they have to be acutely aware that, whatever the science, coatings are also part of the fashion industry.

A good example of the importance of understanding the physics is Carrs Paints' single-pack Glixtone silicate paint, designed for buildings of historic importance. It is a matt, UV-resistant, waterborne paint, which forms a microcrystalline chemical bond with its stone, brick or concrete substrate. It does this without affecting its high vapour permeability and thus its ability to allow damp walls to dry out - and resist freezethaw cycles. It has the usual virtues. It is odourless and incombustible and gives off very little smoke in a building fire. It comes in a good range of colours, retains little dirt, incorporates a fungicide against mould growth and cures rapidly - painters apply it straight from the can and can do two coats in the same day. Carrs is in merger discussions with Blackfriar Paints, which would create synergy with the latter's new water-based Aquaclass stain-blocking paint.

The company has long had a whitespirit-based stain blocker - and found that people had more confidence in this than the idea of a water-based blocker. Blackfriar's Paul Bryan explains that stains migrate because they are soluble in water and in white spirit, and that the answer is to use a less aggressive solvent. But there is nothing less aggressive than water and so the other approach is to use the fact that most paints are strongly alkaline and develop a nonbasic water-based paint, which is less likely to activate the old stain.

One of the advantages of Aquaseal is that contractors can tell if it is going to work after the first coat - rather than having to wait for the whole coating process to be completed.

It doesn't work over limewash or distemper, but Blackfriar has other remedies for these.

On the fashion front, if a building doesn't have a terracotta rain screen it is likely to have Western Red Cedar cladding. But it is a combination of the two that has stormed recent suburban architectural fashion heights. While the terracotta does not need a lot of maintenance, the timber, as the BRE has been pointing out for years, needs protection and regular care.

Ideally, it is said, timber should be protected by an opaque coating because it is degraded by sunlight. But, say designers, that negates the visual pleasures of a natural material and the best compromise is a clear coating or a stain. Unprotected cedar quite soon goes a silver grey colour. However nice that may be, cedar boards in a wall won't necessarily all change colour at the same rate. They can also grow mould and look very unsightly. So should an architect go for maintaining the original honey colour of freshly sawn cedar or for the silver of old walling? Ronseal has understood the dilemma and brought out three colour variations on its waterborne Excel 30 base and 60 finish wood stains. One is light cedar, another dark cedar and a third weathered cedar.

Timber is not alone in needing protection from the elements - metal does, too. The Duke of Westminster's 1824 iron bridge at his Chester estate was recently repainted using ICI metal primer phosphate for spot priming the cleaned metal, followed by two coats of ICI Micaceous Iron Oxide, which is resistant to heavy condensation and humidity, mild chemical attack and atmospheric pollution.

As ever, good preparation, was essential, and it is thought the bridge will not need painting for another decade.

Eight hundred and counting Like Kalzip and DLine, Sto has almost achieved Hoover/Thermos status in UK construction parlance. There are other render systems, but Sto, with its throughcoloured acrylic and silicone-resin renders, has almost single-handedly facilitated the current architectural vogue for retroModern. But it is also used wherever architects want flat surfaces - something they might not have wanted to do because of either the need for expansion breaks or the likelihood that brick-and-blockwork courses would eventually show through.

What is special about Sto is that, because it is reinforced in a variety of ways, it does not crack, nor does it need expansion joints.

British Modernists like white, as Sto ruefully admits. But the company can produce the render in 800 different colours - and a variety of surface textures. Broadway Malyan's Whitelodge day centre at Chertsey is an exuberant example of the possibilities of colour.

In line with current knowledge about water movement in building skins, Sto is vapourpermeable - which is unlikely to be affected by subsequent painting.

Sto has also made inroads in the nowestablished arena of external insulation render, deploying both mineral-fibre insulation boards and expanded-polystyrene foam boards with thicknesses of up to 200mm.

They are fixed either mechanically or by gluing. These external insulation systems all have a reinforcing mesh in the substrate below the decorative finish. This is also a feature of StoRend Flex Cote, which has a special application in refurbishment work, where the performance of the underlying structure may not be entirely understood.

Builders cannot buy Sto off the shelf. The firm has a rigid policy of training and licensing application contractors. There have been reports suggesting that Sto sometimes won't touch small jobs, but the company is adamant that is not possible. It says it licenses contractors across the range, from twoperson operations to companies capable of big-scale application contracts. 'We haven't knowingly turned down a job on grounds of size, ' reassures a Sto spokesperson.

Sto also does internal plasters (and is expected to introduce its European range of paints), but the market leader in interior texture products is Artex, which has just brought out two new products. One is Site Finish designed for new-build projects, and the other is Ceiling Finish for re-patterning existing ceilings. The latter does not attempt the impossible, but offers the prospect of a new flat surface - or a new pattern. Plasterers can sometimes go wild with Artex but it has the enduring virtue of its crack-resistant properties - even with a plain surface.

But is it really waterproof?

Because of the prevalence in Britain of double-skin external wall construction, not much thought is given to the waterproof quality of walls. When the outer skin is a rain screen, it keeps out most water. And whatever water is absorbed it controls, eventually draining it away via the cavity and weep holes or partly back through the external skin - one of the basic arguments for microporous paint systems.

Still, if a masonry surface is too porous it will retain water, and in the wrong weather conditions this freezes and expands.

Following a cycle of freeze-thaw induced expansion and contraction, the surface of masonry, often turned into an impermeable crust by treatments, can be loosened and spall off.

Traditionally, waterproofers are siliconebased, but Keim has developed Lotexan, based on alkoxy silanes. These have a much smaller molecular structure than silicones and can penetrate further into the mineral substrate where, Keim says, they coat its pores. This means water cannot get in but, because pores are not blocked, the materials remain vapour permeable. The company claims a 10- to 15-year life. Equally importantly, Lotexan is matt and clear, so it will not darken masonry or give it a shiny surface.

Watertite is a new, shorter-term solution to the problem of damp in existing walls - in locations such as basements, retaining walls, foundations and concrete slabs. The twocoat, low-odour, oil-based waterproofing resin is mixed with Portland cement, rather than sand, and comes with a five-year guarantee from US-owned and Leeds-based Zinsser UK. It is mould and mildew-resistant, stops efflorescence, can be applied to wet surfaces and dries to an eggshell finish in brilliant white or tinted to various earth and pastel tones. After two weeks, the maximum curing time, the coating is claimed to 'stop 10psi of water pressure - twice the strength of other waterproofers'. And it doesn't smell.

Keeping off ICI Dulux has recently brought out new anti-graffiti paint. It has always had one, but previously only in five whites and off-whites, producing a tough gloss finish. The graffiti is treated with the appropriate spray, left for a few minutes and wiped off. The old range needed care, because the spray could also remove adjacent conventionally painted surfaces. The range has now been extended to 75 colours, all of which are pale because, the company's people note, 'most clients want to brighten up areas - such as subways.'

Dulux's new product, Anti Graffiti Clearcoat, is a clear coating that can be applied over any chosen colour. According to Dulux, 'it means you don't need a whole system - and you can use it over masonry paint'. But because it is chemically complex and not suited to some circumstances, specifiers need to contact the technical advice line, provide details of the proposed use, and its specialists will advise on the appropriateness of its use.

The company says: 'Our reps have details of contractors who can apply it competently.'

Those that don't are put on a blacklist. Ring Dulux on 0870 242 1100, where the advice is cheerful and straight, or go to the online advice centre at www. duluxtrade. co. uk.

Taking it off It is not only paints that are becoming virtuously water-based. One common chemical base for paint strippers is methylene chloride, but ICI Dulux has recently launched three new water-based paint strippers.

The main components of Hydrostrip are water, benzyl alcohol and a bit of hydrocarbon in the form of white spirit. It works, says ICI Dulux, using SARA (selective adhesion release agent) technology. Left on, preferably overnight but for a minimum of six hours to penetrate down to the substrate, Hydrostrip goes through a form of oxidation, which lifts the coating's remaining adhesion, making it easy to scrape or jet-wash off. Several layers of old paint can be removed at the same time.

'There are two things that are important, ' says ICI Dulux. 'The first is how long it is left on and the second is the thickness of the coating - we recommend one-and-a-half times the thickness of the existing coating - and we suggest people carry out a test on a small area.'

Hydrostrip 1000 removes epoxies from metal, 1002 removes coatings from metals and multiple layers from anything, and Hydrostrip 1003 is used for porous substrates, such as wood, masonry and brick.

Claimed cost savings are nearly 30 per cent.

Alternative options There are, of course, alternatives to paint.

Altro is best known for its sheet flooring but it also makes extruded PVC sheet wall covering. It can be used anywhere but the most likely locations are wet areas and where high hygiene standards are called for. The company has brought out 24 new strong colours for its Whiterock Chameleon cladding.

Warranty life is 10 years for the 2.5mm thick sheet, but the claimed life expectancy is more than twice that.

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